1. Field of the Invention
The present invention relates to a method for magnetizing a road marker to provide road information such as the state or form of a road to a vehicle traversing the road. Such road markers are useful for automated piloting of vehicles and other purposes known in the art.
2. Description of the Prior Art
In recent years, various types of technology have evolved for automatically piloting a vehicle. In the typical application, the vehicle is piloted by supplying road information to an electronic unit on the vehicle that controls throttling, steering, and braking. Typical of these devices is the invention by the present inventor described in Japanese Patent Application No. 8-918314.
One of the technologies used for supplying road information is the use of magnetic markers attached to or embedded within a road. Examples of this technology are described in U.S. Pat. No. 5,347,456 and PCT International Publication W.O. No. 92/08176. Magnetic marker technology typically uses a plurality of magnetic markers that have been previously magnetized with an N polarity or an S polarity and are subsequently embedded within a road. The premagnetized markers are embedded in a road so that they create a pattern corresponding to coded road information. By detecting this magnetic pattern, the vehicle detects necessary road information.
While the use of pre-magnetized markers as described above has successfully been used with automatically piloted vehicles, it has several disadvantages. In the first instance, the installation of pre-magnetized markers is precise, tedious work in that the correct spatial placement of correctly polarized markers is critical to system functionality. Also, once embedded, the information conveyed by the marker is fixed making it difficult to upgrade the overall system to provide additional information beyond that originally contemplated. In prior art systems using pre-magnetized markers, changing the information to be conveyed by a marker required digging out the embedded magnetic markers and re-embedding different pre-magnetized markers to properly convey the new road information.
Another disadvantage of the pre-magnetized markers of the prior art is the difficulty in cleaning off iron pieces or iron powder attracted to the marker due to leaked magnetic flux. When a magnetic road marker is embedded in a road and left there for a period of time, many foreign materials are attracted to the place in the road where the magnetic marker is embedded. This has the effect of disturbing the magnetic flux from the marker, which introduces errors into the road information detected by a vehicle.
Some prior art systems tried to correct the foreign material problem by weakening the magnetism of the embedded road marker to a level where, even if materials are naturally attracted to the place in the road where the magnetic marker is embedded, forces of nature are sufficiently strong to remove the foreign material. However, with this configuration, the magnetism of the marker is often so weak that the road information cannot be detected by a vehicle.
To overcome the deficiencies of the prior art, it is a first object of the present invention to provide an in situ road marker magnetizing method so that road markers can be embedded in road surfaces during construction without concern for their magnetic strength or polarization. It is a second object of the present invention to provide an in situ road marker magnetizing method so that the road information conveyed by embedded road markers is easily changed without the need to dig out and re-embed the markers. It is a third object of the present invention to provide an in situ road marker magnetizing method that makes it possible to easily remove foreign materials attracted by leaked magnetic flux while at the same time preserving full magnetic signal strength for reliable information transmission to a vehicle. It is a fourth object of the present invention to provide an in situ road marker magnetizing method that utilizes a magnetizing device mounted in a vehicle dedicated to magnetizing and de-magnetizing road markers and cleaning accumulations of foreign materials attracted to road markers.
To achieve the objects described above, the present invention provides a method for in situ magnetizing of road markers that supply road information to vehicles, consisting of the steps of embedding either pre-magnetized or un-magnetized road markers in a road, and then magnetizing or re-magnetizing the road markers embedded in the road with a pattern corresponding to coded road information.
In one embodiment of the present invention, there is provided a magnetizing unit for magnetizing road markers, a code storing unit for storing codes corresponding to road information, and a magnetization control unit for controlling the magnetizing unit so that a road marker is magnetized in situ according to a pattern corresponding to the code stored in the code storing unit. Each road marker is magnetized in situ by the magnetizing unit so as to create a pattern corresponding to coded road information. With the unit described above, the installation of road markers is greatly simplified due to the elimination of the requirement that road workers carefully embed properly polarized road markers.
Further, in the above-described embodiment, road markers magnetized in situ with the magnetizing unit may also be demagnetized in situ with a demagnetizing unit. Also there may be provided an input unit for inputting the road information to be set into a road marker, and a coding unit for encoding the input road information into an appropriate pattern to be stored in the magnetized road markers. With this configuration, it is possible to update road information by demagnetizing and remagnetizing road markers to a new pattern corresponding to coded road information. This method for updating coded road information is vastly simpler and less costly than digging out and re-embedding pre-magnetized road markers.
It is also possible using the method of the current invention to detect the position of magnetized road markers with a detecting unit. Thus, even when the position of an embedded road marker can not be identified from the road surface, the position can be accurately identified with the detecting unit so that road markers can be reliably magnetized and de-magnetized. This makes possible further efficiencies in the process of constructing roads with embedded markers due to the fact that precise positioning of markers becomes less critical. A further embodiment of the detecting unit places the detection unit within a magnetic field generated by an excitation coil so that the position of road markers can be detected by sensing the change in the excitation coil""s magnetic field.
Foreign materials attracted to a magnetized road marker may be removed with a cleaning unit. In this embodiment, foreign materials such as iron particles or iron powder can be removed, so that magnetic information provided by a road marker is not distorted and accuracy is preserved. In another embodiment, the detecting unit is used to not only detect the location of a road marker, but also to detect a road marker""s polarization and degree of magnetization for maintenance and quality assurance purposes.
A further embodiment of the present invention specifies that magnetic road markers be embedded at standard intervals in the lateral direction across a road. When the magnetic road markers are so spaced, a plurality of magnetizing unit can be similarly spaced so that a plurality of magnetic road markers can be magnetized simultaneously resulting in increased efficiency. In a still further embodiment, a plurality of road markers are embedded along the lateral direction of a road and the magnetizing unit is mounted on the structure of the embodiment so that it can move along the lateral direction of the road. With this configuration, a plurality of road markers embedded along the lateral direction of a road can be magnetized without moving the embodiment of the invention itself A further embodiment of the present invention may be mounted in a vehicle. With this embodiment, magnetizing of road markers occurs as the vehicle passes yielding great efficiency. This efficiency is enhanced in yet another embodiment of the present invention in which the vehicle is automatically piloted.